This application is in response to NCI Program Announcement Number PAR-01-102 for proof of feasibility and development of novel imaging technologies for early detection, screening, diagnosis or image guided treatment of cancer. The ultimate goal of the proposal is to develop a compact, tomographic gamma camera for functional and quantitative imaging of breast cancer. The proposed camera will achieve unprecedented spatial resolution and will be used with a novel gantry system that accommodates complex tomographic orbits to fully sample the breast volume and axillary regions. Statistically based image reconstruction methods that model the physics of the acquisition system and reconstruct complex orbits will provide great flexibility in acquisition and processing system images. The innovative geometrical design will allow measurement of absolute quantitative uptake values and localize lesions in 3D volume. The objective in Phase I will be to construct and characterize the compact high-resolution gamma camera and tomographic gantry and reconstruction system. The performance goals of the system are: a 15 cm x 20 cm camera with intrinsic resolution of 1.5 mm, and a spectral resolution of 10% to 12% FWHM for 140 keV gamma-rays. The optimal tomographic orbits for volumetric breast imaging shall be determined during Phase I. Clinical trials and biopsy guidance will be performed during phase II.